A rotary-type irrigation sprinkler commonly includes a rotatable turret mounted at an upper end of a lower stationary body or other fixed assembly. The turret includes one or more nozzles for distributing water and is commonly rotated through an adjustable arcuate water distribution pattern to provide irrigation over a ground surface area. Rotary sprinklers generally include a drive system, which may include a water-driven motor, to transfer energy of the incoming water into a source of power to rotate the turret. One common mechanism for the motor employs a water-driven turbine and a gear train or gear reduction system to convert a high-speed rotation of the water-driven turbine into relatively low-speed turret rotation. During normal operation, the flow of incoming water into the sprinkler rotates the turbine at a relatively high rotational speed due to the velocity and pressure of the water stream. Then, the gear reduction system converts the relatively high rotational speed of the turbine to a lower rotational speed used to rotate the turret. The gear reduction system commonly includes a number of selected interconnecting gears configured to step down the rotational speed through various gearing ratios. The turret then rotates to distribute water outwardly from the sprinkler nozzles over surrounding terrain in an arcuate pattern.
The most convenient placement for these water-driven motors is usually in the lower stationary portion of the sprinkler assembly, which is upstream of the turret and nozzle. The stationary portion of the sprinkler generally provides the most space to receive the motor and other components of the drive assembly, as the inside of this stationary portion is large enough to hold both the turbine and other gear-reduction components. In this position, however, the entire drive motor and gear train system is located within the water flow path and, therefore, potentially exposed to any dirt or debris in the water, which may work its way into the individual gearing components. Dirt lodged in the gear train and reduction system can damage and limit the useful life of the gearing mechanisms.
If the turbine or gearing becomes damaged, due to the location of the water-driven motor in the stationary body and upstream of the turret, these units are generally not easily accessed in an installed sprinkler system to perform field repairs. Typically, if a gear train becomes damaged, the entire sprinkler assembly including both the turret and stationary body may need to be replaced because the motor generally cannot be accessed in the sprinkler body as a result of the turret components hindering access.
Electrically-driven motors have also been tried in irrigation sprinklers, but the use of electric motors for sprinklers presents challenges and has several shortcomings. For one, providing an electric motor inside the sprinkler housing within the flow of water poses a risk of water entering the motor, which can result in a short and damage to the motor. Typically, shaft seals or other water tight membranes are required to isolate the motor from the water source. Such seals, however, can fail over time resulting in undesired water leakage into the motor. Moreover, supplying sufficient current to run an electrical motor large enough to rotate an irrigation sprinkler turret often requires an external source of electricity to provide the needed current. In this case, there is the disadvantage of routing electrical wires from the external power source, such as an electrical connection to a home or other building, out to the individual sprinkler heads. With the size and complexity of common irrigation systems, routing electrical wiring to each irrigation head adds undesired complexity to the irrigation system.